Superparamagnetic beads have become a helpful tool for biomedical analysis in lab-on-a-chip systems. The polymer shell of the beads can be functionalized with a large variety of chemical groups and biomolecules, allowing, e.g., the targeted capture of specific analytes such as DNA, antigens or antibodies. As the beads are composed of superparamagnetic nanoparticles embedded in a polymer matrix, external magnetic fields can be used to agglomerate or transport beads and bound analytes. With the help of magnetoresistive sensors, the stray field of the beads can be detected, making it possible to use them as markers. However, in all these applications, the bead concentration is usually kept low to prevent particle dipole interactions. Lately, the use of higher concentrations, where dipole interactions take place, has attracted interest. Here, external magnetic fields can be used to form superstructures of interacting beads. These structures can be either 1-, 2- or 3-dimensional, depending on the properties of the magnetic field. Thus, superparamagnetic beads can be used as reconfigurable matter in microfluidic systems, allowing for the assembly and disassembly of simple structures within seconds. These self-assembling structures can then perform specific functions inside the microfluidic channels of the chip, e.g. particle flow control or the formation of reconfigurable sensor surfaces.

In this thesis, the kinetics of this agglomeration into supraparticle structures has been evaluated kinetically. Additionally, four different applications in microfluidic systems have been developed.